In the image film, there are provided continuous image frames and a sound signal recording section along with a large number of perforations bored at a fixed interval along the both side portions in a width direction for the purpose of precisely carrying out frame feed of these image frames. At this sound signal recording section, sound signals are recorded in correspondence with image frames.
In recent cinema systems, there is employed so called a digital sound projection system which has attained enhancement of presence (realism), etc. by stereo sound of more satisfactory sound quality by commonly using not only analog sound but also digital sound. In the image film for such digital sound projection system, a digital sound signal recording section is provided along with an analog sound signal recording section, and a sound signal recording section is constituted by the analog sound signal recording section and the digital sound signal recording section.
Namely, in an image film for digital sound system, respective two left and right perforations are bored in a manner spaced to each other in a feeding direction correspondingly, e.g., every continuous respective image frames. The analog sound signal recording section is provided between one perforations and the image frame, and analog sound signals are recorded therein. Moreover, a pair of left and right digital sound signal recording sections are respectively provided along the area between one perforations and one film side edge and between the other perforations and the other film side edge, and digital sound signals are respectively recorded therein. These digital sound signals are reproduced by a digital sound signal reproducing apparatus 200 which will be described later.
Meanwhile, since an image film for theater of two hours has extensive length which reaches about 18,000 feet or more, the image film was conventionally divided into plural films to respectively wind them on independent film reels. These film reels were alternately mounted on, e.g., two projectors so that screening is carried out. Accordingly, in such a conventional projector system, replacement work and or rewinding work to the projector of film reel, etc. were required. For this reason, many hands were required within a projection room.
In cinema theaters, hands are also short in recent years, and elimination or reduction of labor within the theater is being carried out because reduction of labor cost, etc. Also in the projector system, for the purpose of eliminating replacement work or rewinding work, etc. of a plurality film reels to realize reduction of the number of steps (man-hour) within the projection room, there has been introduced an image film automatic supply/winding unit in which image films are constituted so that they respectively become unitary continuous films every respective titles, and these image films are automatically delivered into a single projector thereafter to rewind them for a second time.
An image film fed out from the image film automatic/winding unit is caused to undergo reading or reproduction of digital sound signals recorded in the digital sound signal recording sections in digital sound signal reproducing apparatus (unit) 200. The digital sound signal reproducing unit 200 is combined with a digital projecting unit (projector), and includes, as shown in FIG. 1, includes a first guide roller 201, a guide sprocket 202, a sound drum 203 and a second guide roller 204 constituting a film traveling path of image film 1 delivered from the image film automatic supply/winding unit. Moreover, the digital sound signal reproducing unit 200 includes first to fourth tension rollers 205 to 208 so that the image film 1 is stably traveled through the traveling path constituent members. An optical reading unit 220 for digital sound which will be described later is provided in association with the sound drum 203.
The first guide roller 201 is disposed at the entrance of the digital sound signal reproducing unit 200 and puts the delivered image film 1 thereon to turn it back (i.e., change its traveling direction) in a horizontal direction. Moreover, the second guide roller 204 is disposed at the exit of the digital sound signal reproducing unit 200 and put the image film 1 thereon to deliver it to the digital projecting unit side. The image film 1 is turned back in a horizontal direction by the first guide roller 201, and is then guided to the sound drum 203 through the second tension roller 206 under the state where the image film 1 is thrust (pushed) on the guide sprocket 202 by the first tension roller 205.
The image film 1 is turned back at the sound drum 203, and is put onto the second guide roller 204 under the state where the image film is thrust (pushed) on the guide sprocket 202 by the third and fourth tension rollers 207 and 208. The second tension roller 206 and the third tension roller 207 are disposed with the film traveling path being put therebetween, and serves to travel the image film 1 in a manner to thrust (push) the image film 1 onto the guide sprocket 202 and the sound drum 203 by elastic (resilient) force of an extension (tension) spring 209 stretched across the respective supporting shafts. It should be noted that tension of the extension spring 209 is very small elastic force, and it is therefore of course that such tension does not constitute hindrance to traveling in the image film traveling path of the image film 1 pulled by the drive sprocket 211 on the digital projecting unit side.
The digital sound signal reproducing unit 200 is not provided with a rotary drive source in the above-described image film traveling path. Accordingly, the image film 1 is caused to undergo, as a drive source, tensile force of the drive sprocket 211 of the digital projecting unit disposed on the succeeding stage side, and is traveled along the image film traveling path within the digital sound signal reproducing unit 200. A flywheel 210 is integrally coaxially provided, as indicated by dotted lines in FIG. 1, on the guide sprocket 202 in order to increase inertia so that it is rotationally operated (actuated) in a stable state.
The guide sprocket 202 has a large number of feed pawls circumferentially provided in a projected manner (hereinafter simply referred to as "projected" depending on circumstances) in a manner spaced in a width direction at the outer circumferential portion thereof, and they are engaged with perforations of the image film 1. Accordingly, the guide sprocket 202 is rotationally operated in counterclockwise direction in FIG. 1 in synchronism with traveling operation of the image film 1 pulled (drawn) by the drive sprocket 211 of the digital projecting unit. Thus, the guide sprocket 202 draws the image film 1 into the digital sound signal reproducing unit 200, and feeds it into the digital projecting unit.
An optical reading unit 220 for digital sound signal is composed of reading light source (not shown), an optical fiber 221, an objective (object lens) section 222, and a CCD line sensor 223. The optical fiber 221 is such that one end portion is positioned in a manner opposite to the reading light source and the other end portion is positioned in a manner opposite to the digital sound recording sections of the image film 1. The objective section 222 and the CCD line sensor 223 are respectively disposed on the optical axis of the optical fiber 221 through the digital sound recording sections of the image film 1.
A digital sound signal recorded in the digital sound signal recording section of the image film 1 is caused to undergo a processing such that rays of light emitted from the light source are guided into the optical fiber 221 and are irradiated onto the digital sound signal recording section, whereby they are respectively focused on the CCD line sensor 223 through the objective section 222 under the state where they are converted into optical light and dark bar code signals.
Meanwhile, in the above-described digital sound projection system, the digital projecting unit and the film automatic supply/winding unit are respectively installed generally in a manner spaced by several meters. For this reason, image film 1 fed out from the film automatic supply/winding unit may undergo a phenomenon such that it hangs down by gravity, or fluctuates by the influence, etc. of slight wind within the projection room. The fluctuating phenomenon of the image film 1 acts as change (fluctuation) of load with respect to the drive sprocket 211 serving as a drive source for pulling (drawing) the image film 1 into the digital projecting unit through the digital sound signal reproducing unit 200, thus producing unevenness of (irregularity) (wow).
As described above, the image film 1 is constituted so that it is held by extremely small force applied when it travels along the image film traveling path having no drive source constructed (provided) in the digital sound signal reproducing unit 200. For this reason, the image film 1 would travels through the image film traveling path under the unstable condition where it is pulsated, as indicated by the portion A of FIG. 1, by rotation of unequal speed of the drive sprocket 211 of the digital projecting section. The flywheel 210 provided at the above-described guide sprocket 202 serves to provide stabilization of traveling state in the image film traveling path of the image film 1 in the case where the image film 1 is delivered in stable state.
While such flywheel 210 effectively acts in the case where image film 1 travels in a relatively stable state, it cannot provide sufficient function for stable traveling of the image film 1 with respect to unevenness of rotation of the drive sprocket 211 resulting from fluctuation phenomenon of the image film 1.
Accordingly, in the above-described digital sound projection system, there were instances in the optical reading section 220 of the digital sound signal reproducing unit 200 where there occurs so called clock shift of digital sound signal such that reading operation of digital sound signals recorded in the digital sound signal recording section of the image film 1 is not precisely carried out. Such clock shift at the time of reproduction of digital sound signal fails to carry out correct reproduction of digital sound signals from the digital sound signal recording section thus giving rise to serious problem, e.g., break (interruption) of reproduction sound.
One measure for solving such problems is to provide, at the entrance side and the exit side of the digital sound signal reproducing unit 200, mechanisms adapted to be rotationally driven in a synchronous manner to drive the image film 1 thus to prevent traveling in the image film traveling path under the unstable condition where the image film 1 is pulsated. However, such drive mechanisms arise problems such that they are required to be driven precisely in synchronism with the film automatic supply/winding unit and the drive sprocket 211 of the digital projection unit, so the digital sound signal reproducing unit 200 are caused to become complicated and enlarged, and it is required to change the fundamental specification of respective units constituting the digital sound projection system to employ a new configuration.
Moreover, another measure is that tension with respect to image film 1 of respective tension rollers 205 and 208 disposed within the digital sound signal reproducing unit 200 is caused to be exerted to more degree, thus allowing the image film 1 to travel the image film 1 in the image film traveling path under the condition where the image film 1 is always stretched. However, in the case such measure for applying large load onto the image film 1 at all times, a large drive source is required in order to travel and drive the image film 1. Eventually, similarly to the above-described measure, a measure such that any drive source is provided in the digital sound signal reproducing unit 200 is required.
In the case where image film 1 is traveled and driven in the image film traveling path under the condition where large load is applied at all times, there might occur problems such that perforations are deformed or broken, and/or the film surface is damaged so that life time of the image film 1 is lowered to much degree. Accordingly, it was impossible to employ measures as described above by any means.
In view of the above, an object of this invention is to provide a digital sound signal reproducing apparatus for a projector, which is adapted for traveling an image film, which is delivered in an unstable condition, in the image film traveling path in a stable state to precisely reproduce digital sound signals recorded in the digital sound signal recording section by digital sound signal reading means.